Nanoparticles, such as carbon nanoparticles, and nanofluids, or fluids containing nanoparticles, have broad industrial application, including use in polymers, liquid polymers/polymer fluids, polymer dispersions, liquid resins, films, coatings films, reinforced polymer composites, transparent electrodes for displays and solar cells, electromagnetic interference shielding, sensors, medical devices and pharmaceutical drug delivery devices. For example, in the field of semiconductors and electronic devices, nanoparticles, and specifically, conductive nanoparticles of carbon, metals and the like, have been known and enabled to the industry for many years. Examples of US Patent disclosures of such particles and processes are provided, by way of non-limiting examples, in U.S. Pat. Nos. 7,078,276; 7,033,416; 6,878,184; 6,833,019; 6,585,796; 6,572,673; 6,372,077. Also, the advantages of having ordered nanoparticles in these applications is well established. (See, for example, U.S. Pat. No. 7,790,560). By way of another example, the combination of nanoparticles and liquid polymers have been found to improve important properties of rubber articles, such as vehicle tires, and in particular, the tread portion of vehicle tires. U.S. Pat. No. 7,829,624.
Nanofluids have also been used extensively in heat transfer fluids, and provide many advantages over prior heat transfer fluids, including thermal conductivities far above those of traditional solid/liquid suspensions, a nonlinear relationship between thermal conductivity and concentration, strongly temperature-dependent thermal conductivity, and a significant increase in critical heat flux. In addition, although conventional heat transfer fluids, such as water, mineral oil, and ethylene glycol play an important role in many industries including power generation, chemical production, air conditioning, transportation, and microelectronics, their inherently low thermal conductivities have hampered the development of energy-efficient heat transfer fluids that are required in a plethora of heat transfer applications. It has been demonstrated recently that the heat transfer properties of these conventional fluids can be significantly enhanced by dispersing nanometer-sized solid particle and fibers (i.e., nanoparticles) in fluids (Eastman, et al., Appl. Phys. Lett. 2001, 78(6), 718; Choi, et al., Appl. Phys. Lett. 2001, 79(14), 2252).). However, there are limitations for these nanofluids as well. For example, in a typical nanofluid, individual nanoparticles, such as carbon nanotubes (CNTs), are irregularly positioned in the nanofluid with only a random and infrequent chance for them to be in contact with each other, and only very high concentrations (e.g., 1 vol % (˜1.4 wt %) of nanoparticle (such as SWNT)) of these nanoparticles seem to produce any noticeable increase in the effective thermal conductivity (Kim, et al., J. Thermophys. Heat Transfer 21 (2007) 451-459; Xie, et al., J. Appl. Phys. 94 (2003) 4967-4971; Hong, et al., J. Thermophys. Heat Transfer 21 (2007) 234-236; Wamkam, et al., J. Appl. Phys. 109 (2011) 024305-024310). However, at these high concentrations, the nanofluid is very viscous and becomes “mud-like,” which makes it much less useful as a coolant or for lubrication applications.
The observed substantial increases in the thermal conductivities of nanofluids can have broad industrial applications and can also potentially generate numerous economical and environmental benefits. Enhancement in the heat transfer ability could translate into high energy efficiency, better performance, and low operating costs. The need for maintenance and repair can also be minimized by developing a nanofluid with a better wear and load-carrying capacity. Consequently, classical heat dissipating systems widely used today can become smaller and lighter, thus resulting in better fuel efficiency, less emission, and a cleaner environment.
Recently, increased thermal conductivity has been associated with exposing fluids with iron oxide-encapsulated nanotubes to a magnetic field. The theory behind this approach is that the magnetic field aligns the iron-oxide encapsulated nanotubes, which results in improved thermal conductivity. Although promising, limitations and unknowns were also revealed. For example, the improved thermal conductivity was found to be sporadic and not observed in every single instance.
Accordingly, there is a great need for the development of nanoparticle mixtures or suspensions and nanofluids that have or result in enhanced properties.